Notes on Evolution (Bio 1)

Notes on the lecture (summer, AY2009-2010) given by Catherine Genevieve B. Lagunzad and this site

Biological and Ecological Gauge of Success

1)      Survivalship
2)      Reproductive success, fecundity (fitness)

The Theory of Inheritance of Acquired Characteristics,
Jean-Baptiste Lamarck

>change over time of successive generations as a population adapts to the environment

>controlled direction of change

 The Theory of Inheritance of Evolution by Natural Selection,
Charles Darwin, Alfred Wallace

                         On the Origin of Species by Means of Natural Selection, Charles Darwin

Influential Factors


i. Uniformitarianism; Geological processes have been uniform through time caused by the same observable processes of today.

ii. Catastrophism; Extinction as a natural biological phenomenon

ii. Gradualism; Accumulated gradual change over vast stretches of time

>The earth is old. It is 4.6 billion years old.
>Observing the present to see the processes of the past
>Slight change over a long time have large impact


Descent with modification; island-mainland life

Overproduction of individuals, Thomas Malthus

>competition for limited resources, struggle for existence
>survival is determined by variations among populations


>some impart greater reproductive success


i. Microevolution, within species

a)      Change in the genetic makeup of a population
b)      Change in the population’s allele or genotype frequencies
c)      Changes within the gene pool of a population

ii. Macroevolution, above species level

>new designs, phylogeny (evolutionary relatedness of organisms)

1)      Fossils > missing links
2)      Biogeography > geographical distribution of organisms
3)      Comparative anatomy

  • modification of shared structures (common ancestor = homologous structures vs analogous structures w/c have different origin but common function)
  • vestigial structures, organs

4)      Comparative embryology
5)      Molecular biology > universal genetic code, but differences in nucleotide base sequence, amino acid sequence (conserved sequences)


1)      Variation

>genetic variation (new characters)

i.      Mutation
ii.      Transposon or jumping genes

>genetic recombination (new combinations of characters)

iii. Synapsis and crossing over
iv. Law of segregation
v. Law of independent assortment of genes

2)      Speciation

  1. Allopatric Speciation > geographic isolation
  2. Sympatric Speciation
  3. Adaptive Radiation > directional selection as a population enters a new habitat with open niches

3)      Phylogeny

>cellular evolution

Natural Selection

>mechanism of evolution
>differential reproductive success that results from the interaction of organisms with their environment
>can amplify or diminish heritable variations
>DNA’s ability to mutate is the fundamental basis for evolutionary change
>populations evolve not individuals
>is situation, direction of evolution is determined by environment, selective forces


a) group of individuals of the same species
b) live together in the same area at the same time
c) exchange genes (reproduce sexually – 3 generations)

Sources of Variation

a)      Mutation > creates new alleles > new traits > new phenotypes
b)      Sexual reproduction > genetic variation in offspring allow some to survive in changing environment
c)      Gene Flow > gain or loss of alleles in a population; immigration, emigration, death

Examples, Types

1)      Stabilizing selection

>favors the intermediate phenotype
>does not lead to change, extremes selected against

2)      Directional selection

>favors extreme phenotype > changes in population > new species

3)      Disruptive (Diversifying) selection

>intermediate phenotype selected against


4)      Sexual selection

>why males and females differ


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